The optimum detection of a signal in the presence of noise isachieved by using matched filter, in the case of FMCW radar thismatched filtering consists of mixing followed by spectrum analysisbased on the FFT. This process in the frequency domain is analogousto the use of matched filtering in the time domain for pulsecompression radar [12]. Fig. 3.6 shows a sample IF signal output intime domain and Fig. 3.7 shows corresponding frequency spectrum ofthe signal. In FFT processing, targets at different ranges appearas different constant frequency components at the mixer outputsignal. The FFT response of the sinusoidal input reveals a mainlobeand sidelobes, as can be seen in Fig. 3.6 and 3.7. The width of themainlobe indicates the Fourier domain resolution. The level of thefirst sidelobe peak relative the mainlobe peak indicates thesusceptibility of weak signals to masking by the sidelobes ofadjacent strong signals. When using the FFT precautions have to betaken to avoid the problems with aliasing, sidelobe generation andpicket fence effect.
- 3 Fast Fourier Transform Processing The Optimum Detection Of A Signal In The Presence Of Noise Is Achieved By Using Matc 1 (393.54 KiB) Viewed 19 times
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PACKARD DIGITIZING OSCILLOSCOPE hp stopped -250.000 us frequency(2) Vp-p(2) LCL HP-MSIB Freq ATTEN 18 dB 18.08 dB/DIV Reptd MARKER Marker BH,Sup Traces State Fig. 3.6 The measured IF signal in time domain Misc PLOT 21:83:37 29.85.2887 RL 8.88 dB SPECTRON ANALYZER 250.000 us 0.00000 s 50.0 us/div current minimum average 45.5455 43.5652 52.7368 47.1731 1.42745 V 1.39608 V 1.42745 V 1.40654 V 48.3 kHz 3.69 d CENTER 58.8 kHz RB 1.88 kHz PRINT #VV VB 1.88 kHz DISPLAY USER 1088 MENU INSTR HOLD delay left TIMEBASE reference -window INSTR PRESET MKR #1 FRQ 48.3 kHz CLEAR 3.65 dB ATA AMIN MRX HOLD A SPAN 100.8 kM MORE ST 385.8 sec 1 of HOLD A STORE trace ABC detectr right on Fig. 3.7 The measured IF signal in frequency domain